There's an old saying about developing world drinking water that goes "If it's brown, drink it down; if it's black, send it back." The plumbing infrastructure in many countries is so poor that clean drinking water is still a precious commodity. Enter the UV-tube, a cheap, portable, solar-powered device that claims to purify five liters of water per minute. Developed by a team at UC Berkeley (from an old potato cannon, it seems), the purifier has been succesfully field-tested in tsunami-ravaged Southeast Asia and is ready for deployment stateside. If you can't wait for the commercial version, try MacGuyvering your own for under $70.